1. Field of the Invention
The present invention relates to a full bridge inverter and, more particularly, to a full bridge inverter controlled by a push/pull control chip to drive a load.
2. Description of Related Art
The power supply for a backlight source of a TFT LCD panel makes use of an inverter circuit to accomplish energy conversion and turn a cold cathode fluorescent lamp (CCFL) on. Conventional inverter circuits can be divided into half bridge-type, full-bridge type and push/pull-type according to different circuit topologies. An inverter circuit is a circuit for converting DC power into AC power.
As shown in FIG. 1, a transformer T1 divides the circuit into a front-end circuit at the first side 101 and a rear-end circuit at the second side 102. The front-end circuit at the first side 101 comprises a DC voltage source Vcc, a first switch Q1, and a second switch Q2. The rear-end circuit at the second side 102 comprises at least a capacitor (C1, C2, C3), a load, and at least a diode (D1, D2). A push/pull control chip 103 is connected between the front-end circuit at the first side 101 and the rear-end circuit at the second side 102.
Reference is also made to FIG. 2 as well as FIG. 1. The push/pull control chip 103 outputs a first control signal a and a second control signal b to turn switching actions of the two switches Q1 and Q2 at the first side 101, respectively. A DC power Vcc is used to provide energy, and the transformer T1 raises and converts the voltage of DC power Vcc to the rear-end circuit 102 for driving the load. The output voltage waveform c at the second side of the transformer T1 is the voltage waveform at point C. As shown in FIG. 2, the output voltage waveform c at the second side is an AC voltage waveform.
In the above description, the push/pull control chip 103 can be the LX1686, LX1688 or LX1691 push/pull control chip produced by Linfinity (Microsemi) Corporation, or the 02-9RR, 0Z9930, 0Z9938 or 0Z9939 push/pull control chip produced by O2 Micro International Limited, or the TL-494 or TL-595 push/pull control chip produced by TEXAS INSTRUMENT, or the BIT3193, BIT3713, BIT3715 or BIT3501 push/pull control chip produced by Beyond Innovation Technology.
As shown in FIG. 3, a transformer T2 divides the circuit into a front-end circuit at the first side 201 and a rear-end circuit at the second side 202. The front-end circuit at the first side 201 comprises four electronic switches (P1, P2, N1, N2), a full bridge control chip 203 and a capacitor C1. Moreover the rear-end circuit at the second side 202 comprises a load.
Referring to FIG. 4, the full bridge control chip 203 transmits four control signals (POUT1, POUT2, NOUT1, NOUT2) to the four electronic switches (P1, P2, N1, N2), respectively; by switching those switches, power is supplied to the load through the transformer T2 according to the DC power. The full bridge control chip 203 is the BIT3105 of the Beyond Innovation Technology Corp or the OZ960, OZ964, OZ9925, OZ9910, OZL68, OZ9938 or OZ9939 of the O2-MICRO Corp.
In the above description, driving the full bridge switch assembly requires the full bridge control chip 203 and driving the push/pull inverter requires the push/pull control chip 103, thus lacking practical flexibility. Furthermore, the control chip of the inverter circuit is limited in use so as to be hard to purchase together.